Re: [PATCH 2/7] dm: Simplify dm_table_determine_type()

[Mike Snitzer <snitzer@redhat.com>]

On Wed, Nov 16 2016 at  3:14pm -0500,
Bart Van Assche <bart.vanassche@sandisk.com> wrote:

> On 11/16/2016 06:54 AM, Mike Snitzer wrote:
> >On Tue, Nov 15 2016 at  6:33pm -0500,
> >Bart Van Assche <bart.vanassche@sandisk.com> wrote:
> >>+/*
> >>+ * Returns true if all paths are blk-mq devices. Returns false if all paths
> >>+ * are single queue block devices or if there are no paths.
> >>+ */
> >
> >This code isn't specific to multipath.  So "paths" is misplaced.
> >"devices" is more appropriate.  Not seeing the need for the comment to
> >be honest.  The function name is pretty descriptive.
> >
> >> bool dm_table_all_blk_mq_devices(struct dm_table *t)
> >> {
> >> 	return t->all_blk_mq;
> 
> Hello Mike,
> 
> After having added WARN_ON_ONCE(sq_count == 0 && mq_count == 0)
> close to the end of dm_table_determine_type() the following output
> appeared:
> 
> WARNING: CPU: 0 PID: 2458 at drivers/md/dm-table.c:966
> dm_table_complete+0x60e/0x6b0 [dm_mod]
> [ ... ]
> Call Trace:
>  [<ffffffff81329b45>] dump_stack+0x68/0x93
>  [<ffffffff810650e6>] __warn+0xc6/0xe0
>  [<ffffffff810651b8>] warn_slowpath_null+0x18/0x20
>  [<ffffffffa0021c8e>] dm_table_complete+0x60e/0x6b0 [dm_mod]
>  [<ffffffffa00245cd>] table_load+0x13d/0x330 [dm_mod]
>  [<ffffffffa0024490>] ? retrieve_status+0x1b0/0x1b0 [dm_mod]
>  [<ffffffffa0025145>] ctl_ioctl+0x1f5/0x520 [dm_mod]
>  [<ffffffffa002547e>] dm_ctl_ioctl+0xe/0x20 [dm_mod]
>  [<ffffffff811f26cf>] do_vfs_ioctl+0x8f/0x6b0
>  [<ffffffff811ff41c>] ? __fget+0x10c/0x200
>  [<ffffffff811ff310>] ? expand_files+0x2a0/0x2a0
>  [<ffffffff811f2d2c>] SyS_ioctl+0x3c/0x70
>  [<ffffffff8163f9aa>] entry_SYSCALL_64_fastpath+0x18/0xad
> 
> Is it intentional that dm_table_determine_type() can get called for
> a dm device with an empty table?

What table were you trying to load when this occurred?

Targets like the 'error' target don't have any devices.